Strain relief bushing



y 1966 F. KLUMPP, JR 3,

STRAIN RELIEF BUSHING Original Filed Nov. 20, 1965 INVENTOR.

j fZ'FD/A/AA/MQUMPEJK iamel United States Patent 3,249,687 STRAIN RELIEFBUSHING Ferdinand Klumpp, Jr., Union, N.J., assignor to HeymanManufacturing Company Continuation of application Ser. No. 325,026, Nov.20, 1963. This application May 28, 1965, Ser. No. 466,497

. Claims. (Cl. 174-153) Strain relief devices are employed in connectionwith various electrical appliances and apparatus such as radio,

television, and many other forms of electrical devices and apparatus,and serve to relieve strain upon the electrical conductor Wires orcables connected thereto so as to avoid possible severance from orimpair proper connection of the conductor wires to terminals to whichthey are normally connected, and to also preclude damage to parts andavoidance of possible short circuits.

In previously available two part strain reliefs, Whether joined or not,used with the old soft wire conductors having relatively thickinsulation, the wire gripped between the parts would cause the parts tospring back so that the flanges or shoulders at one end of the strainrelief would engage opposite sides of the panel into which the strainrelief was inserted.

There is now presently and widely used a thin jacketed stiff conductoror wire which becomes rigidly formed when it is clamped in a two partbushing. There is no spring back to cause the flanges or shoulders ofthe bush! ing to engage a supporting panel and be locked thereon. Thefunctions of clamping the conductor within the bushing and supportingthe conductor and bushing in the panel in locked relationship thereforebecome separate functions independent of each other.

It is desirable to be able to preassemble the strain relief bushing onthe conductor and after the assembly, insert the assembly into the holeor aperture in the panel without the need for a special tool for closingand holding the assembly while pushing it through the aperture in thepanel.

It is also desirable to have a strain relief bushing which is capable ofgripping the insulated wires or conductors over a larger area, henceproviding a better and more firm gripping action. Further, it isdesirable to have such an increased gripping action withoutovercompresof holding the wire is needed. Now the tongue is used onlyfor clamping the wires, and the resilient fingers are used only to holdthe bushing in the hole.

The old locking slot in previous bushing is eliminated in my presentbushing as there is no longer any need for it as the fingers now do allthe locking in the panel.

The use of fingers with more than one step covers a much broader rangeof panel thicknesses than the old constructions. This is an improvementover the old single thickness slot and very necessary to cover thevariety of chassis thickness used by todays appliance manufacturers.

It is therefore an object of my invention to provide an improvedself-locking strain relief bushing particularly suitable for use withthin jacketed stiff wires or conductors and which separates thefunctions of gripping the conductors and locking the gripped conductorsand the bushing in a supporting panel.

Another object of my invention is to provide such a bushing which canbe' manually preassembled on the conductor and the assembly inserted inan aperture in a supporting panel without the use of special tools.

A further object of my invention is to provide such an improved strainrelief bushing having an improved gripping action but which avoidsovercompressing of the wires or conductors, and which completelyinsulates the wires from the panel.

In the drawings:

FIG. 1 is a side elevation of a strain relief bushing made according tomy invention;

FIG. 2 is a left end View of FIG. 1 rotated 90;

FIG. 3 is a right end view of FIG. 1 rotated 90;

FIG. 4 is a plan view of the bushing or grommet in its unassembledrelationship as taken from the mold;

FIG. 5 is a side elevation of FIG. 4;

FIG. 6 shows the relationship of the two parts in an intermediateposition prior to clamping a conductor therebetween prior to assemblywith a conductor;

' FIG. 7 is a plan view of the grommet with a pair of conductorsassembled together and-mounted in a supporting panel; I

FIG. 8 is an enlarged fragmentary view of FIG. 7; and

FIG. 9 is a section taken through FIG. 7 along the line 99.

A strain relief bushing or grommet made according to my inventioncomprises a body portion 10 and an insert sing the conductors which maycause damage to the wire or the strain relief bushing.

The strain relief bushing to be described has separate lockingfunctions; one function is to lock the wire in the strain relief, andthe other is to lock the strain relief in the panel. Separating the twolocking functions satisfies the Underwriters Laboratory 35 pound pullout test on thethin jacket power wires.

All present strain relief bushings utilize the spring back quality ofthe wire to lock the bushing in the panel. However, this spring backtakes away from the locking pressure on the wire. The new power wireshave very thin insulating jackets with practically no resiliency, andtherefore slip more readily through a strain relief bushing and havevery little spring back quality. The spring back action of the strainrelief comes from the resiliency of the insulating jacket of the wire.

Since the new wires lack resiliency and a thick jacket which are neededto hold the UL. test, anew method or grip block 11 co-operatingtherewith, the body portion and grip block providing interconnectedshank sections which may be said to-constitute an axial shank. The bodyportion is provided with a first shank section having flat sides 12 and13 to be received within an appropriate sup porting member, for example,a panel having a properly shaped opening or aperture therein. The flatsides prevent rotation of the bushing in the panel. The body portion hasan end flange or head 14 which abuts the surface of the supportingmember when in use. The body portion may also be made elongated or roundin tranverse section. The body member 10 is provided internally thereinwith a chamber 15 having end walls 17 and 18. The side walls of thechamber 15 are provided with guide channels or grooves 20 and 21extending transversely of the longitudinal axis of the bushing.

Received within the body portion 10 is the insert or grip block 11having a tongue or extension 22 provided with the ribs 24 and 25 whichare received within the channels or keyways 20 and 21. The insert orgrip block 11 is provided with a head or flange portion 14a which abutsthe surface of the supporting member. The flange portion is providedwith shoulders or extensions 11a which abut the surfaces 10a of the bodyportion, when the bushing is assembled,.the surfaces 10a acting as stopsto limit the move- Patented May 3, 1966 ment of the grip block into thechamber 15. The grip block 11 is otherwise shaped to conform to theshape of the body member 10.

v The grip block 11 and body member are integrally joined by theflexible strap or hinge 26. While the hinge or strap 26 is shownconnected to one end of the bushing, it could as well be connected tothe other ends of the two part bushing. It is preferable to have thestrap disposed as shown for appearance sake. The strap is of arcuateform so that it is offset with respect to the conductors clamped betweenthe two parts of the bushing to facilitate assembly. The strap is ofsufiicient length so that the parts may be moved relative to each otherin all planes, there being no great resistance to inserting member 11within member 10 for gripping the conductor 28.

In accordance with my invention, I provide the body portion 10 on theflat sides 12 and 13 thereof with flexible fingers 30 and 31. Thesefingers are fixed at one end and spaced from the flange 14, and extendat an angle to the fiat sides 12 and 13. The free ends or the endsadjacent the flange 14 are each provided with one or more teps orshoulders, 33, 34, 36 and 37. The purpose of these shoulders is toaccommodate the bushing to plates of different thickness. The fingers atthe base portion have some resilience or flexibility so that the bushingmay be pushed through a hole or aperture 41 in the supporting panel 40.As the bushing and conductor clamped therein are forced into theaperture from the left (FIG. 7) the fingers are forced inwardly towardthe axis of the bushing until the flange portions 14 and 14a abut thesurface of panel 40, when the fingers 30 and 31 snap back so that one ofthe shoulders on each finger will engage the plate 40 and lock thebushing in secure position therein.

A strain relief bushing made according to my invention completelyinsulates the conductor from the panel and because of its grippingpower, can withstand more than a thirty-five pound pull test withconductors having the thin jacketed insulation. The strain reliefbushing can be preassembled on the wire and inserted into the aperturein the supporting panel without the need for a tool for this purpost.'Because the grip on the wires or conductors is separated from thelocking action of the bushing in the panel, a strain relief bushingutilizing my invention is more effective in protecting the wires orconductors. There is no loss of pressure on the gripped wire when thestrain relief is inserted and installed in the panel aperture sincethere is no pressure loss which occurs when spring back is relied uponto lock the bushing in the aperture.

The con-ductors or wires are in contact with the walls of the chamberand the tongue of the grip block throughout the entire length of theconductors received within the bushing, thus gripping occurs over alarger area of the bushing and the conductors thus improving thegripping action. Overcompressing is prevented by the built-in safetyconstruction of the shoulders and stop surfaces of the grip block andbody member thus protecting the conductors as the bushing.

If desired afterassembly of the bushing and the conductors, and prior toinsertion in the aperture in the panel, a thin flat retaining ring maybe slipped over the bushing into contact with the flange elements 14 and14a to insure that the assembly is not disturbed while inserting theassembly into the aperture in the supporting panel.

What is claimed is:

1. A strain relief bushing of molded plastic dielectric material adaptedto be inserted axially and snapped into fixed position within acomplementary aperture of a supporting panel, said bushing includingan'axial shank comprising a pair of cooperating shank sections forinsertion within said aperture, one of said shank sections having anaxial Wall with flat sides and being of substantially greatercircumferential extent than the other shank section and providing alongitudinal recess within which the other shank section interfits inclamped position, a head portion carried by each shank section at theextremities oppositely disposed from the entering end thereof having anoutwardly radiating surface for engaging one side of an apertured panel,a resilient finger carried by, spaced from, and overlying at least oneof said fiat sides of said shank sections and fixed to said entering endand spaced axially from the panel-engaging side of said head portions,said finger being outwardly inclined at an angle to the shank sectionsand extending toward and terminating in spaced relationship with respectto the head portions whereby the free end of said finger engages theopposite side of the panel when said bushing is inserted in saidaperture, the juxtapositioned portions of the shank sections and saidhead portions providing a longitudinal passage for accommodating anelongated conductor, and a tongue extending from said other of saidshank sections into said recess for impinging a conductor to secure itin clamped position within the bushing.

2. A one-piece strain relief bushing of molded dielectric materialadapted to be inserted axially and snapped into fixed position within acomplementary aperture of a supporting panel, said bushing including anaxial shank comprising a pair of cooperating shank sections integrallyjoined at their entering extremities by a resilient hinge, the bendingaxis of which traverses the shank axis, said hinge serving to permitjuxtapositioning of said shank sections for insertion within saidaperture, one of said shank sections having a flat side and alongitudinal recess within which the other shank section interfits inclamped position, a head portion carried by each shank section at theextremities oppositely disposed from the enteringend thereof having anoutwardly radiating surface for engaging one side of an apertured panel,a flexible finger fixed to at least one of said shank sections, spacedfrom and overlying said flat side and outwardly inclined toward andterminating in spaced relationship with respect to said head portionsfor engaging the opposite side of the panel, means extending from theother of said shank sections for impinging a conductor to secure it inclamped position within said longitudinal recess, said hinge being ofsuflicient length and of such thickness as to permit ready relativemovement between the shank sections in all planes prior to assembly tofacilitate insertion of said conductor, said hinge having an arcuatelyshaped form to provide an offset loop having no part registering withthe opening projected from the hinge end of said bushing.

3. A one-piece strain relief bushing of molded dielectric materialadapted to be inserted axially and snapped into fixed position within acomplementary aperture of a supporting panel, said bushing including anaxial shank comprising a pair of cooperating shank sections integrallyjoined at one end by a resilient hinge, said hinge serving to permitjuxtapositioning of said shank sections for insertion within saidaperture, one of said shank sections having flat sides and providing alongitudinal recess within which the other shank section interfits inclamped position, a head portion carried by each shank section at thesame extremity thereof and each head portion having an outwardlyradiating surface for engaging one side of an apertured panel, resilientfinger means carried by, spaced from and overlying at least one of saidflat sides of said shank sections and fixed at one end at a positionspaced axially from the panel-engaging side of said head portions, saidfinger means being outwardly inclined at an angle to the shank sectionsand extending toward and terminating in spaced relationship with respectto said head portions whereby the free end of said finger means engagesthe opposite side of the panel when said bushing is inserted in saidaperture, and means extending from said other of said shank section intosaid recess for impinging a conductor received in said bushing to securesaid conductor in clamped position within the bushing, said finger meanshaving stepped shoulders at the free end thereof for engaging the otherside of said panel.

4. A one-piece strain relief grommet of molded plastic dielectricmaterial adapted to be inserted axially and snapped into fixed positionWithin the complementary aperture of a supporting panel, said grommetincluding an axial shank comrising a pair of cooperating shank sectionsintegrally joined at one end by a resilient hinge, said hinge serving topermit iuxtapositioning of said shank sections for insertion within saidaperture, one of said shank sections having a fiat side and asubstantially greater circumferential extent than the other shanksection and providing a longitudinal recess within which the other shanksection interfits in clamped position, a head portion carried by eachshank section at the same extremity thereof and each head portion havingan outwardly radiating surface for engaging one side of an aperturedpanel, resilient finger means integral with at least one of said shanksections, spaced from and overlying said fiat side, and fixed at one endat a position spaced axially from the panel-engaging side of said headportions, said finger means being outwardly inclined at an angle to theshank sections and extending toward and terminating in spacedrelationship with respect to said head portions whereby the free end ofsaid finger means engages the opposite side of the panel when saidgrommet is inserted in said aperture, the juxtapositioned portions ofthe shank sections and said head portions providing a longitudinalpassage for accommodating an elongated conductor, and means extendingfrom said other of said shank section into said recess for impinging aconductor to secure it in clamped position within the grommet, saidhinge being of suflicient length and of such thickness as to permitready relative movement between the shank sections in all planes priorto assembly to facilitate insertion of said conductor.

5. A strain relief bushing of dielectric material adapted '6 r to beinserted axially and snapped into fixed position within a complementaryaperture of a supporting panel, said bushing including an axial shankcomprising a pair of cooperating shank sections integrally joined by aresilient hinge, said hinge serving to permit juxtapositioning of saidshank sections for insertion within said aperture, one of said shanksections having fiat sides and a substantially greater circumferentialextent than the other shank section and providing a longitudinal recessWithin which the other shank section interfits in clamped position, ahead portion carried by each shank section and having an outwardlyradiating surface for engaging one side of said apertured panel,resilient fingers, spaced from and overlying said flat sides outwardlyinclined towards said head portions, integral with at least one of saidshank sections and spaced axially from the panel-engaging side of saidhead portions, the free end of said fingers terminating in spacedrelationship with respect to said head portions and being adapted toengage the opposite side of the panel, and a tongue extending from theother of said shank sections for impinging a conductor clamped betweensaid sections to secure it in clamped position within the bushmg.

References Cited by the Examiner UNITED STATES PATENTS 2,424,757 7/1947Klumpp 174-153 2,424,758 7/ 1947 Klumpp 174-153 2,930,840 3/1960 Klumpp174-153 2,974,186 3/1961 Klumpp 174-153 3,079,581 2/1963 Klumpp 174-153X LARAMIE E, ASKIN, Primary Examiner.

JOHN F. BURNS, Examiner.

1. A STRAIN RELIEF BUSHING OF MOLDED PLASTIC DIELECTRIC MATERIAL ADAPTEDTO BE INSERTED AXIALLY AND SNAPPED INTO FIXED POSITION WITHIN ACOMPLEMENTARY APERTURE OF A SUPPORTING PANEL, SAID BUSHING INCLUDING ANAXIAL SHANK COMPRISING A PAIR OF COOPERATING SHANK SECTIONS FORINSERTION WITHIN SAID APERTURE, ONE OF SAID SHANK SECTIONS HAVING ANAXIAL WALL WITH FLAT SIDES AND BEING OF SUBSTANTIALLY GREATERCIRCUMFERENTIAL EXTENT THAN THE OTHER SHANK SECTION AND PROVIDING ALONGITUDINAL RECESS WITHIN WHICH THE OTHER SHANK SECTION INTERFITS INCLAMPED POSITION, A HEAD PORTION CARRIED BY EACH SHANK SECTION AT THEEXTREMITIES OPPOSITELY DISPOSED FROM THE ENTERING END THEREOF HAVING ANOUTWARDLY RADIATING SURFACE FOR ENGAGING ONE SIDE OF AN APERTURES PANEL,A RESILIENT FINGER CARRIED BY, SPACED FROM, AND OVERLYING AT LEAST ONEOF SAID FLAT SIDES OF SAID SHANK SECTIONS AND FIXED TO SAID ENTERING ENDAND SPACED AXIALLY FROM THE PANEL-ENGAGING SIDE OF SAID HEAD PORTIONS,SAID FINGER BEING OUTWARDLY INCLINED AT AN ANGLE TO THE SHANK SECTIONSAND